THE DIATOMS (BACILLARIOIDEAE) OF NEBRASKA 



BY CLARENCE J. ELMORE 



OCCURRENCE 



Diatoms are found practically in all places where there is water — 

 in lakes, rivers, creeks, ponds, tubs, troughs, tanks ; and on damp 

 ground, rocks, walls, or boards. All water, from the ocean to the 

 smallest puddle caused by the tracks of cattle's feet, provided the 

 puddles persist for a few days, is almost certain to contain diatoms. 

 When unmixed with other substances they present a brownish 

 color. Often the entire bottom of a stream may be covered to a 

 thickness of an inch or more with a brown mass of diatoms. But 

 the greater number occur mixed with other algae, in which case 

 their brown color is hidden by the green of the algae. 



Diatoms are also found in the fossil state. In this condition 

 they are called Diatomite by geologists, or Kieselguhr in com- 

 merce. The name Infusorial Earth has also been applied to them, 

 but this is incorrect, for diatoms are not Infusoria. 



Diatoms differ from other plants in that their cell walls are thor- 

 oughly infiltrated with silica, or quartz of the opal variety. The 

 form of the cell is often likened to a pill box or a telescope, one- 

 half fitting over the other. The statement made in practically all 

 of the textbooks is that when a cell divides the two valves, ends of 

 the cell, separate slightly and a new valve grows inside of each, 

 thus forming two new cells. Thus each new cell has one of the 

 original valves of the mother cell and a new valve formed inside 

 of the girdle of the old one. Hence it would appear that one of 

 the new cells is the exact size of the mother cell and the other 

 slightly smaller, the reduction in size going on with each cell divi- 

 sion. This process continues until a certain minimum size is 

 reached, when an auxospore is formed. The necessity for auxo- 

 spore formation arises from the fact that the cell walls of diatoms 

 are silicified and so can not grow, together with the fact that they 

 become smaller with each division. 



Volume 8, The Nebraska Geological Survey published by the University 

 Studies, Volume 21 



